Semiconductor memory device

ABSTRACT

A DRAM performs data writing if a column activation signal ZCOLRE is activated with changing of an internal address Add and then an internal write control signal WDRV is activated by generation of a write signal WE from an outside. However, in order to solve a problem that data writing does not performed in some cases when the data writing is performed at optional timing, a semiconductor memory device according to the present invention includes a delay unit, thereby delaying an output of the internal write control signal WDRV until the column activation signal ZCOLRE is activated, even when the write signal WE is generated.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an internal timing in data write to a semiconductor memory device.

[0003] 2. Description of the Related Art

[0004] In the case where a memory cell is a DRAM type, when write is carried out at an arbitrary timing as SRAM, there is the case where no data write is carried out, and error write is generated.

[0005] In this type of memory device, as shown in FIG. 7, in the case where a chip enable signal M-CE# is an “L” level, when a change occurs in an address Add, which is an external address signal, the memory device is actuated by receiving the change. The following is a description on the case where an external write signal WE# (# is indicative of being an L level and active) is activated in the latter half of a cycle of the address Add. With the change of the address signal Add, an address transition detection signal ATD is generated, and thereafter, in accordance with a fall of the address transition detection signal ATD, a row activation signal INTZPAS, a word activation signal RXT, a sense amplifier activation signal SO and a column activation signal ZCOLRE are activated in succession.

[0006] On the other hand, as shown in FIG. 7, when the external write signal WE# is generated in the latter half of a cycle of the address Add, in accordance with the generation of the external write signal, an internal write signal INTWE is activated. After a predetermined time elapses from the activation, an internal write control signal WDRV is activated. At the point of time when the WDRV signal is activated, the column activation signal ZCOLRE is already activated; therefore, write of data DQ is carried out according to the internal write control signal WDRV.

[0007] Next, the following is a description on the case where the external write signal WE# is activated in the former half of a cycle of the address Add, as shown in FIG. 8. In this case, like the case of FIG. 7, with the change of the address Add, the address transition detection signal ATD, the row activation signal INTZPAS, the word activation signal RXT, the sense amplifier activation signal SO and the column activation signal ZCOLRE are activated in succession.

[0008] On the other hand, in accordance with the generation of the external write signal WE#, the internal write signal INTWE is activated, and then, after a predetermined time elapses from the activation, the internal write control signal WDRV is activated. However, in this case, at the point of time when the WDRV signal is activated, the column activation signal ZCOLRE is not activated yet; for this reason, the write of data DQ is not carried out according to the internal write control signal WDRV.

[0009] Moreover, as shown in FIG. 9, there is the case where a short cycle shorter than a normal cycle is generated by any factors. The short cycle is not conformable to the standard design; therefore, no write is carried out. The following is a description on the case where the external write signal WE# is generated for the period of the short cycle, and thereafter, a normal read cycle is carried out.

[0010] In the shirt cycle, the internal write control signal WDRV is activated in accordance with the generation of the external write signal WE#. For this reason, when the column activation signal ZCOLRE is activated (as shown by a dotted line) in the above short cycle, unnecessary write is carried out; as a result, error write is generated.

[0011] Usually, a design is made so that the write failure and error write are not generated. However, in the case where a write circuit is simply designed and internal write is carried out based on external write timing, when a design mistake is added, the above-mentioned write failure and error write are generated.

[0012] An object of the present invention is to provide a memory device, which can carry out a normal write in a normal cycle without generating error write in various write timings.

SUMMARY OF THE INVENTION

[0013] In a DRAM, data write is carries out when a column activation signal ZCOLRE is activated with a change of an internal address Add and an internal write control signal WDRV is activated by a generation of an external write signal WE. However, when the data write is carried out at an arbitrary timing, no data write is carried out in some cases.

[0014] In order to solve the above problem, according to a first aspect of the present invention, a semiconductor memory device includes a delay unit for delaying an output of the internal write control signal WDRV until the column activation signal ZCOLRE is activated even if the write signal WE is generated.

[0015] Moreover, in the case where the external write signal WE# is generated under the short cycle, when the column activation signal ZCOLRE is activated in the prior cycle, a problem arises such that error write is generated. In order to solve the above problem, according to a second aspect of the present invention, a semiconductor memory device includes a non-activation unit for non-activating the internal write control signal WDRV by a change of the address signal of the next cycle when the external write signal WE# is inputted under a short cycle in which the external address signal is inputted in a short period shorter than a predetermined period.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a block diagram showing a semiconductor memory device according to a first embodiment of the present invention;

[0017]FIG. 2 is a circuit diagram showing a detail configuration of a WDRV generating circuit shown in FIG. 1;

[0018]FIG. 3 is a circuit diagram showing a detail configuration of a shift circuit shown in FIG. 2;

[0019]FIG. 4 is a time chart showing an operation of the present invention;

[0020]FIG. 5 is a time chart showing an operation of the present invention;

[0021]FIG. 6 is a time chart showing an operation of the present invention;

[0022]FIG. 7 is a time chart showing an operation of a conventional semiconductor memory device;

[0023]FIG. 8 is a time chart showing an operation of a conventional semiconductor memory device; and

[0024]FIG. 9 is a time chart showing an operation of a conventional semiconductor memory device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0025] First Embodiment

[0026]FIG. 1 is a block diagram showing a semiconductor memory device according to a first embodiment of the present invention. A clock generating circuit 61 generates an internal clock by a chip enable signal M-CE#, which is an external control signal, an output enable signal OE#, an external write signal WE#, a low-order byte data control signal LB# and an upper-order byte data control signal UB#. A memory cell 62 is a DRAM type, and has an input/output interface being compatible with an asynchronous SRAM, and further, controls read, write and refresh operations of the clock generating circuit 61. Further, the memory cell 62 is a fully hidden refresh type (refresh operation is not seen from the outside), and a refresh control by external clock and system usually has no need.

[0027] Read is carried out in the following manner; more specifically, in a state that an M-CE# terminal is in an “L” level and both of a LB# terminal and a UB# terminal or either of them is in an “L” level, a WE# terminal is set to an “H” level and an OE# terminal is set to an “L” level. Thereafter, when an address is designated by external address signals A0 to A20 inputted to a row address buffer and a column address buffer shown in FIG. 1, a designated address data is outputted to a data input/output pin DQ (DQ0 to DQ15) terminal.

[0028] Further, in the case where the read is carried out in a state that the LB# terminal is set to “L” and the UB# terminal is set to “H”, the read data is outputted to the input/output pins DQ0 to DQ7, and the input/output pins DQ8 to DQ15 become high impedance. On the other hand, in the case where the read is carried out in a state that the LB# terminal is set to “H” and the UB# terminal is set to “L”, the read data is outputted to the input/output pins DQ8 to DQ15, and the input/output pins DQ0 to DQ7 become high impedance.

[0029] Furthermore, in the case where the read is carried out in a state that both of the LB# terminal and the UB# terminal is set to “L”, the read data is outputted to the input/output pins DQ0 to DQ15. In the read cycle, the address is always captured in the present device when the signal M-CE# is an “L” level, and then, the read data is outputted.

[0030] Write is carried out in the following manner; more specifically, when the M-CE# terminal is in an “L” level state and both of the LB# terminal and the UB# terminal or either of them is in an “L” level state, the WE# terminal is set to an “L” level. Thereafter, when an address is designated, the data inputted from the DQ terminal is written into the designated address of the memory cell 62. In the case where the write is carried out in a state that the LB# terminal is set to “L” and the UB# terminal is set to “H”, the data inputted from the DQ0 to DQ7 is written; on the other hand, the data from the DQ8 to DQ15 is neglected.

[0031] Further, in the case where the write is carried out in a state that the LB# terminal is set to “H” and the UB# terminal is set to “L”, the data inputted from the DQ8 to DQ15 is written; on the other hand, the data from the DQ0 to DQ7 is neglected. In addition, in the case where the write is carried out in a state that both of the LB# terminal and the UB# terminal are set to “L”, the data inputted from the DQ0 to DQ15 is written.

[0032] Furthermore, in the case where both of the WE# terminal and the OE# terminal are set to an “L” level, the write operation is overridden. The address in writing is controlled so as not to have a change for the period when the signal WE# is an “L” level. The signal WE# rises up, and thereafter, the address can be changed.

[0033]FIG. 2 shows an internal write control signal WDRV generating circuit 60 included in the clock generating circuit 61 of FIG. 1. The WDRV generating circuit 60 carries out a control using the following signals generated by other control circuits. In other words, the WDRV generating circuit 60 delays an internal write signal INTWE so as to generate an internal write control signal WDRV.

[0034] The above using signals are an internal write signal INTWE, a column control signal ZCOLRE and an address transition detection signal ZRATD. More specifically, the internal write signal INTWE is generated based on the external write signal WE#. The column control signal ZCOLRE is generated based on the address Add of the address signal, and activates a column circuit when and the chip enable signal M-CE# are inputted to an external address pin Ai (i=0 to 20). The address transition detection signal ZRATD is generated in accordance with a change of the address Add. Thus, the WDRV generating circuit 60 generates the internal write control signal WDRV.

[0035]FIG. 3 shows a circuit configuration of a shift circuit 3 of FIG. 2. The shift circuit 3 carries out a control using the following signal generated by other control circuits.

[0036] The above using signals are a column control signal ZCOLRE, an address transition detection signal ZRATD, and a write early set signal ZCASWSF, which has a specific delay and is generated based on the internal write signal INTWE. The shift circuit 3 generates a write set signal ZCASWS, which is a trigger signal of the internal write control signal WDRV.

[0037]FIG. 4 is a time chart showing a normal write timing (write signal WE# is activated in the latter half of the address cycle). The present semiconductor memory device is operated when a change of the address Add occurs in the case where the chip enable signal M-CE# is an “L” level as described above. With the change of the address Add, the address transition detection signal ATD is generated, and then, in accordance with the fall of the signal ATD, a row activation signal INTZRAS, a word activation signal RXT, a sense amplifier activation signal SO, and a column activation signal ZCOLRE are activated in succession. More specifically, the row activation signal INTZRAS activates a row circuit for generating a row address based on the change of the address Add of the chip enable signal M-CE#. The word activation signal RXT activates a word line following the activation of the row activation signal INTZRAS. The sense amplifier activation signal SO activates a read sense amplifier following the activation of the word activation signal RXT. As described above, a predetermined time is necessary until the column activation signal ZCOLRE is activated from the change of the address Add.

[0038] On the other hand, in accordance with the external write signal WE#, the internal write signal INTWE is activated, and thereafter, the activated signal is inputted to a head one-shot 1 for generating an “L” level one-shot pulse when the internal write signal INTWE rises up. Then, in accordance with the rise of an output node RS_FF_OUT1 of a reset-set flip-flop circuit RS_FF1, the write early set signal ZCASWSF is outputted from a head one-shot 2 after a predetermined time, and then, is inputted to the shift circuit 3.

[0039] As shown in FIG. 3, the shift circuit 3 outputs (activates) the write set signal ZCASWS when the column activation signal ZCOLRE is activated in the case where the write early set signal ZCASWSF is outputted (activated). However, when the column activation signal ZCOLRE is non-active, the shift circuit 3 outputs the write set signal ZCASWS after the column activation signal ZCOLRE is activated.

[0040] At the point of time when the write early set signal ZCASWSF is inputted, the column activation signal ZCOLRE is already activated; therefore, the shift circuit 3 outputs the write set signal ZCASWS immediately when the write early set signal ZCASWSF is inputted thereto.

[0041] An internal signal CDEW is activated by the activation of the write set signal ZCASWS, thereby the internal write signal WDRV is activated. At this point of time, the column activation signal ZCOLRE is activated; therefore, the write of data DQ is carried out. Subsequently, the internal write control signal WDRV is non-activated since the chip enable signal M-CE# is an “H” level.

[0042]FIG. 5 is a time chart showing the case where the external write signal WE# is activated in the former half of cycle of the address Add. The external write signal WE# is activated at the same time with a change of the address Add, and then, the data DQ is inputted, and further, the internal write signal INTWE is activated. By the activation of the INTWE signal, the write early set signal ZCASWSF is set like the case of FIG. 3. However, at this point of time, the column activation signal ZCOLRE is non-active; for this reason, the write set signal ZCASWS is not set.

[0043] On the other hand, with the change of the address Add, the address transition detection signal ATD, the row activation signal INTZRAS, the word activation signal RXT, the sense amplifier activation signal SO, and the column activation signal ZCOLRE are activated in succession.

[0044] At the point of time when the column activation signal ZCOLRE is activated, the write set signal ZCASWS is set. By the activation of the write set signal ZCASWS, the internal signal CDEW is activated, thereby the internal write signal WDRV is activated. At this point time, the column activation signal ZCOLRE is activated; for this reason, the data is written from the data input-output pin DQ.

[0045] As described above, even if the write early set signal ZCASWSF is set, the shift circuit 3 does not output the write set signal ZCASWS immediately, and outputs the write set signal ZCASWS after the column activation signal ZCOLRE is activated; therefore, the write after that is permitted.

[0046]FIG. 6 is a timing chart showing a timing in the case where the write signal WE# is generated for the period of a shirt cycle in which the address signal changes in a period shorter than a predetermined period. In this case, the cycle means the period between the change of address signal and the next change thereof. The data is inputted from the data output pin DQ at the same time with the change of the address signal. In accordance with the generation of the external write signal WE#, the internal write signal INTWE is activated, and then, the write early set signal ZCASWSF is set. However, at this point of time, the column activation signal ZCOLRE is non-active; therefore, no write set signal ZCASWS is outputted.

[0047] In accordance with the change of the next address Add, the address transition detection signals ATD and ZRATD are generated. When receiving the signal ATD, the shift circuit 3 generates a row activation signal INTZRAS. The row activation signal INTZRAS is reset in the next address change.

[0048] In the case where the next address Add changes at a timing earlier than a timing when the column activation signal ZCOLRE is activated, with the address change, the shift circuit 3 generates the address transition detection signal ATD and a signal ZRATD, which is a reversal signal to the ATD. By doing so, a shift reset signal SHIFT_RESET signal is generated; on the other hand, the write set signal ZCASWS is not set. For this reason, the internal write control signal WDRV is not activated; therefore, the data write is not carried out. As described above, the shift circuit 3 of FIG. 2 functions as a non-activating unit for non-activating the internal write control signal WDRV in the case where the external write signal is inputted in the short cycle.

[0049] As is evident from the above description, according to a first aspect of the present invention, the semiconductor memory device includes a delay unit for delaying the output of the internal write control signal until the column activation signal is activated even if the write signal is generated. Therefore, at the point of time when the write signal is generated, it is possible to solve a problem that no write is carried out because the column activation signal is not activated.

[0050] According to a second aspect of the present invention, the delay unit outputs a write set signal, which is a trigger signal of the internal write control signal in the case where the internal write signal is activated and the column activation signal is activated. Further, in the case where the internal write signal is activated and the column activation signal is non-active, the delay unit outputs the write set signal after the column activation signal is activated, so that the internal write control signal can be activated according to an output of the write set signal. Therefore, it is possible to realize a semiconductor memory device by a simple logic device.

[0051] According to a third aspect of the present invention, the semiconductor memory device includes a non-activation unit for non-activating the internal write control signal by a change of the external address signal of the next cycle when the external write signal is inputted under a short cycle in which the external address signal is inputted in a period shorter than a predetermined period. Therefore, it is possible to prevent error write even if the write signal is generated under the short cycle.

[0052] According to a fourth aspect of the present invention, in the case where a change of the next address occurs at a timing earlier than a timing when the column activation signal is activated, the non-activation unit generates an address transition detection signal with the change of the external address signal, and outputs no write set signal, so that the internal write control signal is not activated. Therefore, it is possible to realize a semiconductor memory device by a simple logic device. 

What is claimed is:
 1. A semiconductor memory device comprising: a memory cell array having a memory cell arranged in a matrix; and a row address circuit and a column address circuit for carrying out a write operation with respect to a memory cell having an address corresponding to an external address signal, the semiconductor memory device writing a data inputted from the outside to a memory cell having the corresponding address when a column activation signal for activating the column address circuit with a change of the external address signal is activated, and simultaneously or after that, when an external write control signal is inputted, so that an internal write signal is activated, the semiconductor memory device further comprising delay means for delaying the activation of the internal write control signal until the column activation signal is activated even if the write signal is generated.
 2. A semiconductor memory device according to claim 1, wherein the delay means outputs a write set signal, which is a trigger signal of the internal write control signal in the case where the internal write signal is activated and the column activation signal is activated, and outputs the write set signal after the column activation signal is activated in the case where the internal write signal is activated and the column activation signal is non-active, so that the internal write control signal can be activated in accordance with an output of the write set signal.
 3. A semiconductor memory device comprising: a memory cell array having a memory cell arrayed in a matrix; and a row address circuit and a column address circuit for carrying out a write operation with respect to a memory cell having an address corresponding to an external address signal, the semiconductor memory device writing a data inputted from the outside to a memory cell having the corresponding address when a column activation signal for activating the column address circuit with a change of the external address signal, and simultaneously or after that, when an external write control signal is inputted so that an internal write signal is activated, the semiconductor memory device further comprising non-activating means for non-activating the internal write control signal by a change of the address signal of the next cycle when the external write signal is inputted under a short cycle in which the external address signal is inputted in a period shorter than a predetermined period.
 4. A semiconductor memory device according to claim 3, wherein in the case where a change of the next address occurs at a timing earlier than a timing when the column activation signal is activated, the non-activation means generates an address transition detection signal with the change of the external address signal, and outputs no write set signal, so that the internal write control signal is not activated. 